O'Reilly logo
  • Rickard Korkko thinks this is interesting:

Acknowledgment Number is a 32-bit field that identifies the sequence number the source next expects to receive from the destination.

From

Cover of Routing TCP/IP, Volume 1, 2/e

Note

What's the TCP acknowledgement number field used for? #TCP url:https://www.safaribooksonline.com/library/view/routing-tcpip-volume/1587052024/graphics/01fig17.gif